Evaluation of an early-stage prototype polyurethane femoral head implant for hip arthroplasty

Abstract

Introduction: Thi study evalautes a new bone-preserving femoral head cover that mimics the articular cartilage of the femoral head.

Methods: A specially developed polyurethane (PU) was evaluated in biocompatibility (cytotoxicity test) and mechanical response to tensile loading. In the cytotoxicity test, steam sterilized (SS) and ethylene oxide sterilized (EtO) PU samples were incubated separately in a cell culture medium. The seeded cell line MG-63 was then added to these sample-incubated cell culture mediums. One negative control group and one positive control group were also evaluated. The cells in each group were cultured for seven days before being quantified using the alamarBlue assay. In the mechanical test, the femoral head cover implants were separated into three groups of three samples. Each group represented a different implant insertion idea: direct insertion (uc sample) and another two insertion modes (is and ss samples) representing implants with enclosure mechanisms. The test consisted of distance-controlled cyclic tensile loadings followed by a failure test.

Results: The cytotoxicity test results show no significant difference in fluorescence intensity between the negative control, the three SS groups, and one EtO group (P > 0.05). However, the other two EtO groups exhibit significantly lower fluorescence intensity compared with the negative control (P < 0.05). In the mechanical test, the is samples have the highest cyclic loading force at 559.50 ± 51.41 N, while the uc samples exhibit the highest force in the failure test at 632.16 ± 50.55 N. There are no significant differences (P > 0.05) among the uc, is, and ss groups in terms of stiffness.

Conclusion: The cytotoxicity test and the mechanical experiment provide initial assessments of the proposed PU femoral head cover implant. The evaluation outcomes of this study could serve as a foundation for developing more functional design and testing methods, utilizing numerical simulations, and developing animal/clinical trials in the future.

Keywords: Bearings; Hip arthroplasty; Implant; Polyurethane.

Fig. 1

Conceptual design of a femoral head implant during insertion (left) and wrapped around (right) the femoral head, preserving bone and femoral head ligament.

Fig. 2

Geometry of the PU sample for biocompatibility test (top) and mechanical test (bottom).

Fig. 3

Experimental setup with upper and lower c-arm parts, which pull the femoral head apart. The three femoral head cover setups are (a) uncut/without suture (uc), (b) with simple interrupted suture (is), and (c) with running subcutaneous suture (ss).

Fig. 4

AlamarBlue assay results of each group on Day 1, Day 2, Day 4, and Day 7 (* P > 0.05 in comparison to the negative control on Day 7).

Fig. 5

Left: Force-displacement diagram of femoral head cover (a) uncut/without suture (uc), (b) with simple interrupted suture (is), and (c) with running subcutaneous suture (ss).

Fig. 6

Example of load to failure curve comparing the three different implants.